The present invention relates to a process for producing .epsilon.-caprolactam and more particularly, to a process for producing .epsilon.-caprolactam from cyclohexanone oxime, characterized by using a crystalline zeolite having a specific pore size or a crystalline zeolite having closed pores.
.epsilon.-Caprolactam is an important raw material for nylon and the like and has, hitherto, been produced by liquid phase Beckmann rearrangement of cyclohexanone oxime using fuming sulfuric acid or concentrated sulfuric acid as a catalyst.
However, this process suffers from the problems such as need of fuming sulfuric acid in a large amount and by-production of ammonium sulfate in a large amount.
For solving these problems, it has been proposed to carry out gas-phase rearrangement using solid catalysts such as crystalline zeolites, for example, ZSM-5 (Japanese Patent Application Kokai Nos. 57-139062 and 62-123167). In this case, however, the selectivity for .epsilon.-caprolactam formation and the like are not enough and further improvement in this respect has been demanded.
Under the circumstances, in order to find a further improved process for producing .epsilon.-caprolactam, the inventors have conducted intensive research on crystalline zeolites as catalysts. As a result, it has been found that cyclohexanone oxime adsorbed into the pores of the zeolites brings about side reaction to cause reduction in the selectivity and it has been further found that the selectivity for .epsilon.-caprolactam formation is remarkably improved by using crystalline zeolites having a specific pore size or crystalline zeolites having closed pores.